1. Technical Field
The present invention pertains to a piston ring with a groove seal on a ring flank of the piston ring. The present invention more specifically pertains to a piston ring with a flexible material that is recessed in a groove, wherein the material seals the lower flank of the piston ring, i.e. the far flank referred to the combustion chamber or the piston head.
2. Related Art
Piston rings and, in particular, compression rings are typically used in the first (top) and in the second (central) piston ring groove of internal combustion engines. The function of the compression ring is characterized by the following properties:    1.Sealing the crankcase against the combustion gases.    2.Stripping off excess lubricating oil such that as little lubricating oil as possible remains on the inner cylinder wall and can be combusted.
Rings with a crowned design of the contact surface are used for this purpose. In a compression ring, the majority of the gas not only flows in the direction of the crankcase via the joint, but depending on wall thickness and diameter also via the lower ring flank. This gas flow is nowadays primarily caused by the surface roughness and waviness of the piston ring flank and the piston ring groove flank in the contact regions. Depending on the temperature influence, a deformation of the piston groove can also occur and negatively affect the seal.
It is known to design compression rings in a symmetric or symmetrically crowned fashion with a respective maximum contact point on the contact surface. In this case, the piston ring groove flanks and the piston ring flanks are manufactured with a defined surface roughness in order to give the piston rings a defined mobility in the circumferential direction. Neither the waviness of the piston ring groove nor the waviness of the piston ring itself is usually taken into consideration.
Known piston rings are disclosed, for example, in patent applications DE102010034870 A1 and DE19942241 A1. DE102010034870 A1 discloses piston rings with through-holes in the axial direction such that the wall thickness of the piston ring is purposefully weakened, wherein this purposeful weakening of the wall thickness is most effective, in particular, if the bores are produced in the vicinity of the extreme fiber, in this case near the inside diameter of the piston ring. DE19942241 A1 discloses a piston ring groove with a chrome coating on a piston ring groove flank. DE19942241 A1